Compound microscope and lens system therefor



MrhAQ, 1943. A. wARMlsl-IAM 2,335450 (NVH'OUNDv MICRCSCOPE AND LENSSYSTEM THEREFOR Filed Jan. 23, 1941 /C Fig. i 4 C l /f F\ F- A A2 lg-Qkc E J /Q s m T a VC l Fig. i

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Y Patented Mar. 9, 1943V COMPOUND MICROBCOPE AND LENS SYSTEM THEREFORArthur Warmisham, Leicester, England, assignor to Kapella Limited,Leicester, England, a company of Great Britain Application January 23,1941, Serial No. 375,684 In Great Britain January 23, 1940 (o1. srs-svi17 Claims.

This invention relates to compound microscopes and more particularly toa lens system, correctedfor chromatic aberrations, astigmatism, iieldcurvature and distortion, such as may be used as the ocular thereof. Acompound microscope normally consists of an objective for forming aprlmary'image of the object in the plane of a diaphragm, and an ocularcomprising a convergent eld lens adjacent to the primary image plane inconjunction with a convergent eyelens.

It is often preferred in practice to observe an image projected on to ascreen rather than to employ a microscope in the usual way with directvisual observation, and in particular it may be desired to project theimage of the profile of an object on to a master drawing, in order todetermine whether the object has the correct shape or dimensions. Theuse of a compound microscope for such purpose has the advantage ofgiving a high magnication ratio with a relatively small distance betweenthe object and the projection screen, but existing microscope ocularsusually have a considerable residue of uncorrected distortion whichobviously makes them unsuitable for the purpose of comparison of theimage with a master drawing.

The present invention has for its primary object to provide a lenssystem suitable for use as a projection ocular for a compound microscopeand having improved distortion correction and gold oblique colourcorrection.

The lens system. according to lthe invention conveniently comprises aconvergent field lens, and a convergent eyelens lsystem whole focallength lies between 115 and 140 per cent of the equivalent focal lengthof the complete lens system and whose axial thickness is not less than60 per cent of the equivalent focal length of the complete lens system.It is to be noted that the term eyelens system is employed herein todenote the lens or lenses cooperating with the field lens to form theocular, entirely irrespective of whether a single lens or more than onelens is employed'. In fact, the convergent eyelens system preferablycomprises at least two airseparated convergent components, and in oneconvenient arrangement consists of two compound components separated byan airgap.

Such a lens system, when used as the ocular of a compound microscope,has its field lens disposed adjacent to the primary image plane of theobjective of the microscope. The exit pupil of the ocular preferablylies either within the eyelens system or at a distance behind the rearsurface of the eyelens system not greater than 15 per cent of theequivalent focal length of the ocular. In one convenient form theobjective of the microscope is arranged in the manner described inBritish patent specification No. 444,350, and comprises two convergentcomponents, of which the rst is a field member adapted to form an imageof the light source at the entrance pupil of the second component whichacts to correct the outstandirigv aberrations of the rst component.

The invention may be carried into practice in various ways, but theaccompanying drawing illustrates by way of example a preferredarrangement of compound microscope according thereto intended forprojection purposes, with three alternative forms of ocular for usetherein. In the drawing,

Figure l diagrammatcally illustrates the complete microscope,

Figure 2 shows one convenient form of objective for use in themicroscope of Figure l, and

Figures 3 to 5 show the three alternative forms of ocular for use in themicroscope of Figure l.

In this arrangement the objective, indicated at A in Figure l and shownin detail in Figure 2, forms its primary image of an object at B in theplane C of a diaphragm, and a graticule Cl is provided in this primaryimage plane C. The ocular E, shown in detail in three alternative formsin Figures 3 to 5, may be regarded as a development of the well-knownRamsden eyepiece, and serves to project on to a screen F superimposedimages of the object B and of the graticule Cl. One important use, towhich this arrangement may be put, is to determine the correctness ofshape of the prole of an object by comparing it with a master drawing,and in this case the projection screen F will itself bear the masterdrawing and the graticule C1 will serve to enable accurate measurementsto be made of any errors in the shape of the proi'lle. Alternatively,the graticule Cl may consist of shaped markings and may itself serve inplace of a master drawing, the superimposed images on the screen F thuspermitting comparison of the prole with the graticule markings. It willbe appreciated that for such purposes it is important that the projectedimage should be substantially free from distortion and oblique colour,and the primary purpose of the invention is so to improve an eyepiece ofthe Ramsden type as to correct for the distortion usually presenttherein.

It isof course important that the objective A should be such as to givea primary image well-corrected for distortion and other aberrations andan objective of the kind described in the above-mentioned British patentspecification No. 444,350 is satisfactory for this purpose. One exampleof objective of this kind is shown in Figure 2 and comprises twocollective members A1A. The first member A1 consists of an achromatiseddoublet corrected for distortion and images the light source at theentrance pupil of the second member-A2. This second member isself-corrected for chromatic aberrations and distortion and servestocorrect the outstanding aberrations of the first member A1. The secondmember may conveniently'consist of an anastigmat lens comprising adispersive component placed between two collective components.

The ocular E, of which three examples are shown respectively in Figures3,.,4 and 5, coml prises a iield lens E1 in the form of a simpleconvergent element disposed adjacent to the primary image plane C of theobjective A anden the rear side thereof (i. e., the side further fromthe objective) and an eyelens system E2 which is of substantial axialthickness and is preferably achromatic and consists of two convergentcompound components separated by an airgap, each component having oneinternal cemented surface. The exit pupil of the ocular E will usuallylie within the eyelens system E2 thereof, but in some instances the exitpupil may lie a short distance behind the rear surface of the eyelenssystem.

Numerical data for the three 'examples of ocular shown in Figures 3 to 5are given in the following tables, in which RaRa represent respectivelythe radii of curvature of the individual lens surfaces counting from thefront (the positive sign indicating that the surface is convex to thefront and the negative sign that it is concave thereto), DiDz representthe thicknesses of the individual lens elements along the axis, and S182represent the axial airgaps between the components. VThe tables alsogive the mean refractive index no and Abb V number of the glass used foreach element. The equivalent focal length ofthe ocular is in eachexample taken as unity.

Example Il Thickness Refractive Ahh V mms pugno index 'un number Rx m 'Dx=.120 1.511) 611.3 Rz= (176 Sl 495 RJ 94() Dz=.175 1.613 59.3 R4 (138D:i=. 029 1. 652 33. i R5= +5. 33

S2=. 576 Rt= +1. 92

Example I I I Thickness Refractive Abb V 1mdk Sepauon index 'nn numhorRl: m

Dl=. 106 1. 511) 60. 21 R2 5971 D3=. 027 1.652 33. 5 Rr= +4. 708

' Sz=. 667 Rs +4. 708

D4= 026 1. G52 33. 5 R1= 5638 D5=.153 1.013 50.3 Rs 1. 433

The distances of the fiat front surface (R1) of the field lens E1respectively from the exit pupil of the objective A and from theinternal focal plane C of the microscope are in Example I 4.00 and .186,in Example II 4.13 and .196 and in Example III 3.44 and .458. The totalaxial thickness of the eyelens E2 is in Example I .945, in Example II.857 and in Example III 1.026. The equivalent focal length of theeyelens system E is lin Example I 1.27, in Example II 1.267 and inExample III 1.26 so that the power of the eyelens system is in eachexample between 78 and of the power of the complete ocular E. The exitpupil of the ocular E lies within the eyelens system E2 in Examples Iand II'I and. a short distance outside the eyelens system in Example II,the position being in Example I .032 inside the rear surface (R8), inExample II .044 behind the rear surface (Ra) and in Example III .042 infront of the front surface (Ra) of the rear component.

It will be appreciated that the foregoing arrangement can be modified invarious ways within the scope of the invention, for example, byemploying a simple element in place of one of the compound components ofthe eyelens or again by employing more than two components for theeyelens system.

What I claim as my invention and desire to secure by Letters Patent is:

1. A lens system, corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular of a compoundmicroscope, comprising in combination in axial alignment a convergentfield lens, and a convergent eyelens system whose focal length liesbetween and 140 per cent of the equivalent focal length of the completeocular lens system and whose axial thickness is not less than 60 percent of the equivalent focal length of the complete lens system.

2. A lens system as claimed in claim 1, in which the eyelens systemcomprises at least two air-separated convergent components.

3. A lens system as claimed in claim 1, in which the eyeiens systemconsists of two compound convergent components separated by an air gap.

4. A lens system. corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular of a compoundmicroscope as set forth in 4claim 1, wherein the exit pupil of theocular is separated from the rear surface of the eyeiens system by adistance not greater than per cent of the equivalent focal length of thecomplete ocular lens system.

5. A lens system, corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular oi' a compoundmicroscope, comprising in combination in axial alignment a convergentfield lens, and a convergent eyeiens system whose focal length liesbetween 115 and 140 per cent of the equivalent focal length of thecomplete ocular lens system and wherein the exit pupil of the ocularlies within the eyeiens system thereof, said eyelens system comprisingtwo air-separated compound convergent components with an axial thicknessnot less than 60 per cent of the equivalent focal length of the completeocular lens system.

6. A lens system, corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular of a. compoundmicroscope, comprising in combination in axial alignment a convergentfield lens, and a convergent .eyeiens system whose focal length liesbetween 115 and 140 per cent of the equivalent focal length of thecomplete ocular lens system and wherein the exit pupil of the ocularlies behind the rear surface of the eyeiens system at a distance notgreater than 15 per cent of the equivalent focal length of thercompleteocular lens system, said eyeiens system comprising two air-separatedcompound convergent components with an axial thickness not less than 60per cent of the equivalent focal length of the complete ocular lenssystem.

7. A lens system, corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular of awcompoundmicroscope, comprising in combination in axial alignment a convergentfield lens, and a convergent eyelens system whose focal length liesbetween 115 and 140 per cent of the equivalent focal length of thecomplete ocular lens system and wherein the exit pupil of the ocularlies within the eyeiens system thereof.

8. A lens system, corrected for chromatic aberrations, astigmatism,field curvature and distortion, for use as the ocular of a compoundmicroscope, comprising in combination in axial alignment a convergentfield lens, and a convergent eyeiens system whose focal length liesbetween 115 and 140 per cent of the equivalent focal length of thecomplete ocular lens system and wherein the exit pupil of the ocularlies behind the rear surface of the eyeiens system at a distance notgreater than 15 per cent of the equivalent focal length of the completeocular lens system.

9. A compound microscope, comprising in combination an objective, and anocular consisting of a convergent field lens and a convergent eyelenssystem, the field lens being disposed adjacent to the primary imageplane of the objective, whilst the focal length of the eyeiens systemlies between 115 and 140 per cent ofthe equivalent focal length of thewhole ocular, the exit pupil of the ocular being separated from the rearsurface of the eyeiens system by a distance not greater than 15 per centof the equivalent focal length of the complete ocular.

10. A compound microscope as claimed in claim 11, in which the objectivecomprises two convergent components, of which the first is a fieldmember acting to form an image of the light source at the entrance pupilof the second component, which acts to correct the outstandingaberrations of the first component.

11. A compound microscope, comprising in combination an objective, andan ocular consisting of a convergent field lens and a convergent eyeienssystem, the field lens being disposed adjacent to the primary imageplane of the objective, whilst the eyeiens system has a focal lengthlying between and 140 per cent of the equivalent focal length of thewhole ocular` and axial thickness not less than 60 per cent of theequivalent focal length of the complete ocular, the exit pupil of theocular being separated from the rear surface of the eyelens system by adistance not greater than 15 per cent of the equivaient focal length ofthe complete ocular.

12. A compound microscope, comprising in combination an objective, andan ocular consisting of a convergent field lens, and a convergenteyeiens system whose focal length lies between 115 and 140 per cent ofthe equivalent focal length of the complete ocular lens system and whoseaxial thickness is not less than 60 per cent of the equivalent focallength of the complete lens system, the field lens being disposedadjacent to the primary image plane of the objective, whilst the exitpupil of the ocular lies within the eyeiens system thereof.

13. A compound microscope as claimed in claim 11, in which the objectivecomprises two convergent components, of which the first is a fieldmember acting to form an image of the light source at the entrance pupilof the second component, which acts to correct the outstandf ingaberrations of the first component, whilst the eyeiens system of theocular comprises at least two air-separated convergent components.

14. A compound microscope as claimed in claim 12, in which the objectivecomprises two convergent components, of which the first is a fieldmember acting to form an image of the light source at the entrance pupilof the second component, which acts to correct the outstandingaberrations of the f irst component, whilst the eyeiens system of theocular comprises at least two air-separated convergent components.

15. A lens system for use as the ocular of a compound microscope havingnumerical data substantially as set forth in the following table:

Radius Thfne Refractive Abb V separation dex np number Ri= D Di=.115 1.519 60. 3 R2== 650 D22. 16S l. 613 59. 3 R: 613 D o s e 2 1. 52 33. 5

Sz=. 553 Raz-P5. 12 D 028 D5=.168 1. G13 59. 3 Ra=1. 433

wherein R1R2 indicate the radii of the individual individual elements,and S1S2 the axial air sepasurfaces, DlDz the axial thickness of therations between the components. individual elements, and SiS: the axialair sepa- 17. A lens system .for use as the ocular of a rations betweenthe components. compound microscope having numerical data 16. A lenssystem for use as the ocular of a 5 substantially as set forth in thefollowing table: compound microscope having numerical data substantiallyas set forth in the following table:

Thickness Refractive Abbev Radius or Separation index nn numberThickness .Refractive Abb V 10 Radius or separation ind "D umher R1D1=.1o5 1.519 50.3

S1=l.43 R1= Ra=+.sa25

D,=. 12o 1. 519 m. a D,=. 153 1. 513 59. a Rz=.676 15 R4H-.5638

$11495 D12, 027 1. 552 sa. 5 Rs=+.940 R55=+L 708 112:. 175 1. 613 59. 3SF, 657 R1=. Gas RFM vos Da=. 029 1. 552 sa. 5 D.=. 02a 1. 552 as. 5R,=+5. 33 121:4. 553s s2=. 51e D1=.15a 1. 613 59. 3 R=+1.92 20 12F-1.433

D1=. 029 1. 552 3a. 5 R1=+.638

' D5=. 048 1.613 59. 3 12F-2.92 wherein R1R2 indicate the radii of theindividual surfaces, 131D: the axial thickness of the 25 individualelements, and S1511 the axial air sepawherein RiRz indicate the radii ofthe individual rations between the components. surfaces, D1D2 the axialthickness of the ARTHUR WARMISHAM.

